Older sea ice is thicker and more resilient to melting than new ice. Old ice is generated over years and new ice generally melts away each summer. What's alarming is that this video shows the dramatic decline of important 'old' ice.
In 1988, ice that was at least 4 years old accounted 26% of the Arctic’s sea ice. But by last year, ice of that age accounted for only 7% of all Arctic sea ice.
Popular Science say the decline could be explained by the fact that white ice reflects light, and discourages surface warming. But dark, ice-free water absorbs more solar radiation, leading to more heating.
This video shows how the volume of sea ice has gone down since 1987.
The YouTube video description explains what you are watching:
"The winter ice pack in the Arctic was once dominated by multi-year*, thick ice. Today, very little old ice remains. This animation shows maps of sea ice age from 1987 through the end of October 2013. Age class 1 means "first-year ice," which is ice that formed in the most recent winter. The oldest ice (9+) is ice that is more than 9 years old. Animation by NOAA climate.gov, based on research data provided by Mark Tschudi, CCAR, University of Colorado.
*Revised on 2/21/14. Caption originally said "old." Revised to "multi-year" to reduce ambiguity."
